It has recently been discovered, and is elsewhere patented, that lower organic compounds containing hetero-atoms, such as oxygen, sulfur and/or halogen, are convertible over a special class of crystalline zeolite catalysts at elevated temperatures to form hydrocarbons in the gasoline boiling range. This conversion is carried out at a temperature in the range of about 500 to 1200.degree. F, preferably at temperature in the range of about 650 to 850.degree. F at space velocities in the range of about 0.5 to 50 LHSV. The product obtained comprises water, light hydrocarbon gases (C.sub.4.sup.-) and a normally liquid hydrocarbon fraction (C.sub.5.sup.+) which contains a substantial amount, usually at least about half, of C.sub.6 to C.sub.10 monocyclic aromatic hydrocarbons.
It is also known and elsewhere disclosed that with a one carbon feed such as methanol, a portion of the produced aromatic hydrocarbons is durene (1,2,4,5 tetramethyl benzene). Durene is an undesirable component of gasoline because of its high melting point (174.7.degree. F) and its tendency to crystallize out of solution at temperatures below 175.degree. F. It has previously been recognized that one can increase the production of durene by carrying out the above described conversion at superatmospheric pressures. As an engineering matter, it is sometimes desirable to operate an industrial process of this type at elevated pressure. In this particular methanol operation, there are also some process advantages to be gained by operating at superatmospheric pressure. However, with the pressure responsive production of durene, substantial process operating compromises need to be made in order to produce a quality gasoline with an acceptably low durene content.